De-aeration of sealing fluid in aerated rotary fluid machines



May 31; 1966 R. s. SPROULE 3,253,816

DE-AERATION 0F SEALING FLUID IN AERATED ROTARY FLUID MACHINES FiledMarch 12, 1965 c/ im INVENTOR 5 fl-ll ROBERT S. SPROULE F/G. 2 BY amu QDay/91* ATTORNEYS United States Patent 3,253,816 DE-AERATION 0F SEALINGFLUID 1N AERATED ROTARY FLUID MACHINES Robert S. Sproule, Montreal,Quebec, Canada, assignor to Dominion Engineering Works Ltd., Montreal,

Quebec, Canada Filed Mar. 12, 1965, Ser. No. 439,274 3 Claims. (Cl.253-26) The present invention relates to rotary fluid-machines, such aspumps and pump turbines of the type which have shrouded impellers, meansto aerate the spaces surrounding the shrouds and means to prevent airfrom escaping into the impeller intake.

In rotary hydraulic machines it is customary to provide seals whichprevent excessive quantities of working fluid from leaking past theimpeller by way of the clearances between the impeller and thestationary structure. The working fluid which unavoidably leaks throughthese seals passes into the main stream of working fluid at somelocation adjacent to the intake side of the impeller. In machines whichhave aerated shroud spaces for reducing fluid friction, the fluidescaping through the seals can serve as a barrier to the unintentionedescape of air from the shroud spaces, in which case, any air which doesescape from the shroud spaces, passes with the discharged seal waterinto the main stream of working'fluid.

Air passing into the main stream of working fluid is of littleconsequence where the machine is operating as a turbine. However, if themachine is operating as apump, the escaping air will enter the impellerand, if in excess, will seriously affect the operating etficiency of themachine.

There have been prior art methods, such as disclosed in German Patent714,290, designed to cope with the problem of limiting the quantity ofescaping air which reaches the impeller inlet. This patent discloses aleakoff chamber which is separated from the low pressure area adjacentto the impeller inlet by a space seal; this seal is supplied withworking fluid under pressure. This method is not fully effective for thefollowing reasons: Firstly, the air-water mixture in both the leak-offchamber and the space-seal is rotated due to the fluid friction dragfrom the rotating impeller shroud. This results in centrifugalseparation of the air and water whereby the.

lighter component, i.e. air, is urged toward the axis of rotation of themachine. The air leakage path along the clearance of the space seal tothe area of the impeller intake is such, that the air moves freely intothe impeller intake, because at no point does the leakage path increasein radius to utilize the force of centrifugal separation to impede theescaping air rather than assist it to escape. A secondary defect is thatseparation of air and water occurs on the high pressure side of therunner seal so that the solubility of air in the water it contacts ishigh, hence the effectiveness of separation is considerably reduced bythe large amount of air that the water retains in solution. Thesubsequent leakage of air-saturated water past the seal results in therelease of alarge quantity of air in the low pressure space at theimpeller intake.

The disadvantages of prior art are overcome in the .present invention bythe provision of an air collection chamber on the low pressure side ofthe impeller seals, with an air removal system, in conjunction with astructure such that the leak-off path for air to the impeller intakeoffers considerably more resistance to any air flow than that offered bythe designed removal path. This is achieved by making some part of theescape path from the collection chamber to the impeller intake on anincreasing radius from the axis of rotation in order to utilize thedirectional separating effect of centrifugal action.

Patented May 31, 1966 According to the present invention there isprovided in a rotary fluid machine, which incorporates an aeratedshrouded impeller, space seals supplied with working fluid underpressure together with radial extensions on the impeller shrouds, andair collection chambers for the removal of air. The air collectionchambers are disposed between the low pressure side of the impellerseals and the impeller extensions. These radial extensions, acting incooperating relationship with the stationary part of the machine, formpassageways which offer considerably more resistance to the escape ofair than to the escape of liquid because of the directional separatingeffect of centrifugal action. v

In co-pending US. patent application Serial No. 357,448, filed April 6,1964, there is described an aerated notary fluid machine in Which theescape path of any excess of air supplied to the shroud spaces isthrough the seals to the are-a adjacent to the impeller intake. Thepresent invention will be described as incorporated in this type ofmachine but it will be readily understood that the incorporation of theteachings herein described to other types of aerated rotary fluidmachines falls within the scope of the present invention.

The primary object of the present invention is to provide an economicalmeans whereby air leakage from the shroud spaces of an aerated rotaryfluid machine is prevented from entering the impeller intake in suchquantity as to significantly affect the performance of the machine.

A further object of the present invention is to provide on both the bandshroud and crown shroud of a rotary impeller at locations adjacent tothe low pressure sides of the band and crown seals respectively, radialextensions which project outwards from the axis of rotation of theimpeller into annular spaces provided in the stationary structure, suchthat the maximum diameter of these extensions is greater than thediameter at the exits of the fluid seals.

Other objects and many of the attendant advantages of the presentinvention will become more readily apparent upon consideration of thefollowing detailed specification in connection with the accompanyingdrawings wherein:

FIG. 1 is a partial sectional view of an impeller and stationary casingembodying the present invention and;

FIG. 2 is an enlarged sectional view of a portion of the rotary machineshown in FIG. 1.

Referring now to the drawings and with particular reference to FIG. 1,when the machine is operated as a pump, a source of external power isapplied todrive shaft 4 which is attached to the impeller assembly. Therotating assembly comprises crown shroud 1 and band shroud 2 which areconnected to each other by a plurality of blades 3. In the operation ofthe rotating impeller assembly as a pump, water is pumped from a lowpressure at the inlet shown generally at 5 and is dis charged at ahigher pressure into a volute casing 6. Conventional close clearancespace seals are shown at 8 on crown shroud 1 and at 7 on band shroud 2.Extending from the axial peripheries on the crown and band shrouds 1 and2, are radial extensions 9 and 10 respectively. These radial extensionsare attached to and rotate with the impeller assembly in annularrecessed portions 11- element of band seal 7, by radial surface 18, byradial wall 22 and axial wall 23 of stationary structure 26.

Parallel surfaces 20 and 21 of shroud 2 of stationary structure 26respectively, delineate a horizontal annular space 24 which is open toinlet 5.

When the machine is operated as a pump, shroud compartment 27 will beaerated by air supply pipe 31 according to the disclosure set forth inco-pending application Serial No. 357,448. There will be a continuousflow of water through peripheral gap 29 and through the passageways 34,35, 36 and 37, to supply sealing water to seal 7. Excess of air, abovethat which is required for aeration of compartment 27, is discharged byway of-annular pasageways 38 and 39 into chamber 36, where it is thenconveyed by the sealing water by way of passageway 37 through seal 7, tochamber 11.

As the impeller assembly revolves, rotating surface 18 tends to causethe air-water mixture in chamber 11 to rotate, whereby centrifugal forcewill urge the lighter air portion of the mixture toward surface 17 wherean escape path is provided by way of conduit 13 to manifold 15. Space 24is bounded by the horizontal surface 20 of the impeller and rectangularfaces 21 and 23 of stationary structure 26, while being accesible to thefluid present at adjacent to the impeller intake. It is manifest thatrotation of the impeller causes a drag and hence rotation, to begenerated in the fluid space 24. Consequently there is a pressurebuild-up in the region of face 23 and rotating surface 19, imparted bythe centrifugal force of the fluid. Necessarily, the pressure at face 23is significantly higher than in region 5. This pressure build-up isconducive to the evacuation of the air-Water mixture through conduit 13.

In the case of a single stage machine or the low pressure stage of amulti-stage machine, the air-water mixture in manifold 15 can bedirected to a separator (not shown) from which the air is discharged toatmosphere and the water is recycled to the machine intake. In the caseof high pressure stages of a multiple stage machine the air and water ofthe air-water mixture can be separated at such pressures that they aresuitable for aeration and sealing operation respectively, for the lowerpressure stages.

It can be seen that in accordance with the present invention there isprovided a'rotary fluid machine, having aerated impeller shrouds, withmeans for preventing the air from passing into the main stream of theworking fluid. In the disclosed embodiment the means for achieving thisresult comprises radial extensions on both the band shroud and the crownshroud of the impeller which are so disposed that the air separated bycentrifugal action tends to follow the path of least resistance to theleak-off chambers, rather than around the increased radius of the radialextensions and into the impeller intake.

While particular embodiments of the invention have been illustrated anddescribed with reference to a hydraulic pump using water as the workingfluid and air in the shroud chambers, it will be obvious to thoseskilled in the art that various changes and modifications may be madeWithout departing from the spirit of the invention. For example, thepresent invention could be applied to a pump with a working fluid ofcrude oil, utilizing gases in the shroud compartment which must notcontaminate the working fluid.

I claim: 1

1. In a rotary fluid machine comprising a stationary housing, a rotatingmember, said rotating member comprising axially spaced upper and lowershrouds having a plurality of blades secured therebetween and defining afluid flow channel, said stationary housing forming shroud spacesbetween the said upper and lower shrouds and said housing, means forintroducing air to the shroud spaces, radial extensions on the impellershrouds for providing a path of flow from the shroud spaces to theimpeller intake on an increasing radius, and means for withdrawing airand water mixture disposed adjacent the radial extensions, the radialextensions acting as a barrier to the flow of air into the impellerintake from the shroud spaces. 2. A rotary fluid machine according toclaim 1 and further including fluid seal means comprising restrictedpassageways formed at each end of the shroud spaces to limit the inflowof fluid from the impeller passageway into the shroud spaces.

3. A rotary fluid machine according to claim 1 wherein the inlets forthe air withdrawing means are disposed adjacent the area of least radiusof the radial extensions whereby air escaping from the shroud spaces aremixing with the fluid tends to be separated from the fluid bycentrifugal force and passes through the inlets of the air withdrawingmeans.

References Cited by the Examiner UNITED STATES PATENTS 3,174,719 3/1965Sproule et all 253-26

1. IN A ROTARY FLUID MACHINE COMPRISING A STATIONARY HOUSING, A ROTATINGMEMBER, SAID ROTATING MEMBER COMPRISING AXIALLY SPACED UPPER AND LOWERSHROUDS HAVING A PLURALITY OF BLADES SECURED THEREBETWEEN AND DEFINING AFLUID FLOW CHANNEL, SAID STATIONARY HOUSING FORMING SHROUD SPACESBETWEEN THE SAID UPPER AND LOWER SHROUDS AND SAID HOUSING, MEANS FORINTRODUCING AIR TO THE SHROUD SPACES, RADIAL EXTENSIONS ON THE IMPELLERSHROUS FOR PROVIDING A PATH OF FLOW FROM THE SHROUD SPACES TO THEIMPELLER INTAKE ON AN INCREASING RADIUS, AND MEANS FOR WITHDRAWING AIRAND WATER MIXTURE DISPOSED ADJACENT THE RADIAL EXTENSIONS, THE RADIALEXTENSIONS ACTING AS A BARRIE TO THE FLOW OF AIR INTO THE IMPELLERINTAKE FROM THE SHROUD SPACES.